You can use the commands above to import it to your local machine and push it to github.
You can push and pull to git and also commit (dcommit) and update (rebase) to subversion from there.

Please note: A git repository allows no partial checkouts like subversion does, therefore I've imported only the yiiext/ subfolder as an own repo, not your complete svn.
But you can work around this gltich by creating, i.e. a yiiext-app repo and include the code in extensions/yiiext/ also as a submodule. But submodules act as a normal git repo within your parent project.

Please let me know if you have other thoughts or an alternative for this problem.

Website is finished: http://yiiext.github.com/
You'll find all yiiext extensions with downloads, readme in russian and english.
Issue tracker is on github for every single repository and is linked from the website.

Technical Background:
The Website is built by a yii application that creates the github pages with data from the github api every night ran by a jenkins-ci server.

I didn't get it: so http://yiiext.github.com/ is a yii repository site that concentrates all Yii extensions that are managed on github?

I'm asking since the site shows only 53 extensions while AFAIK there are hundreds already.

(This isn't intended to look down on the effort and the initiative - on the contrary! I just want to understand it better. I was actually looking for a site that concentrates info about Yii extensions with a useful UI. http://drupalmodules.com/ is a good example, for the Drupal world).

No, it's not.
It's a project managed by a talented team of developers.
It's by far the only extensions there is.
Use the extension repository from Yiiframework.com (Download - Extensions) if you want the full list of all extensions.